Cell Structure and Metabolic Regulation 



35 



aspects of carbohydrate metabolism. This particular topic 

 makes a good subject for cytochemical speculation because, 

 of all the metabolic processes, most is known about the 

 reactions involved in carbohydrate metabolism. Let us now 

 note what is known about the localization of the enzymes 

 involved, particularly those catalysing the steps between 

 glycogen and triose phosphate. Of these, phosphorylase and 

 phosphoglucomutase (cf. de Duve and Berthet, 1954), 

 glucose-6-phosphate dehydrogenase (cf. de Duve and Berthet, 

 1954; Newburgh and Cheldelin, 1956) have been found in the 



Fig. 13. Schematic representation of the possible role of the ER in some 

 aspects of carbohydrate metabolism. 



supernatant fluid along with aldolase. Because glycolysis 

 can take place in the supernatant fluid, all the glycolytic 

 enzymes are presumed to occur in this fraction (cf. de Duve 

 and Berthet, 1954). Glucose-6-phosphatase is one of the few 

 enzymes which has been exclusively localized in the micro- 

 some fraction (cf. de Duve and Berthet, 1954). The localiza- 

 tion of hexokinase is controversial (cf. Siekevitz and Potter, 

 1955). As mentioned above, two auxiliary enzymes, the 

 DPNH and the TPNH-cytochrome c reductases, are found in 

 the microsomes as well as in the mitochondria. 



Fig. 13 is an entirely theoretical scheme, based on very few 

 observations, but including those mentioned above. I am 

 purposefully exaggerating the morphological component of 

 cellular metabolism in the hope that while I will undoubtedly 



